Motor vehicle gearbox

ABSTRACT

Motor vehicle gearbox, comprising an input shaft (2) and two countershafts (3, 4) having six pairs of interengaging gears (7-11, 15, 16, 17-20) for first to sixth gear. The disengageable gear (17) for the first gear speed engages a disengageable gear (23) on the fourth shaft (5) for reverse.

This invention is related to International Application PCT/SE95/00226filed Mar. 3, 1995, entitled "Motor Vehicle Gearbox".

BACKGROUND OF THE INVENTION

The present invention relates to a motor vehicle gearbox comprising ahousing with an input shaft and two countershafts lying in a planeoffset from the input shaft and having gears in engagement with gears onthe input shaft, at least one gear of each pair of mutually engaginggears on said shafts being disengageable from its shaft, one of saiddisengageable gears being mounted on one countershaft and being disposedto transmit torque in the first gear speed to a final drive unit.

DESCRIPTION OF THE RELATED ART

A gearbox of the above described type is known, for example, bySE-A-8601247-3. It has five gear speeds forward and one reverse. Thetorque is transmitted in reverse from the input shaft via onecountershaft to the other countershaft. In this way, the need for aseparate shaft for the idler gear for reverse is eliminated. Instead,the first mentioned countershaft is used as a reverse gear shaft. Thisprovides a particularly compact, simple and inexpensive design, which,with its axially small dimensions is particularly suited for usetogether with transverse engines.

SUMMARY OF THE INVENTION

The purpose of the present invention, starting from the above describedgearbox, is to achieve a gearbox, which in a five-speed version can bemade even shorter, and, in a six-speed version, will be as short as theknown five-speed gearbox.

This is achieved according to the invention by virtue of the fact thatthe input shaft has at least five gears in engagement with gears on thecountershafts for transferring torque to the final drive unit forforward drive with at least five different gear ratios, and that thedisengageable gear for transmitting torque in the first gear speedengages an additional gear which is disengageably carried on a fourthshaft and is disposed to transmit reversing torque to the final driveunit.

In a six-speed embodiment of the gearbox according to the invention, theinput shaft has six gears in engagement with gears on the countershafts.

In this embodiment, a disengageable gear for the sixth gear speed canassume the place taken by the reverse disengageable gear in a five-speedgearbox, and the reverse disengageable gear can instead be carried by anextra shaft. In comparison with the above mentioned known five-speedgearbox, one gear is eliminated in the drive train in reverse by virtueof the fact that the reverse disengageable gear on the fourth shaftengages directly the disengageable gear for the first gear speed andnow, as in the known design, a gear solidly joined to the hub of thedisengageable gear for the first gear speed. This also providesoptimally small masses to be synchronized and a suitable gear levershift pattern is obtained.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described in more detail below with reference toexamples shown in the accompanying drawing, where

FIG. 1 shows a schematic longitudinal section through a five-speedgearbox according to the invention,

FIG. 2 is a longitudinal section through one embodiment of a six-speedgearbox according to the invention, and

FIG. 3 is a schematic end view of the gearbox shown in FIG. 2, and

FIG. 4 shows the shift lever shift pattern.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In a gearbox housing generally designated 1, which also forms thehousing for the clutch, an input shaft 2, a first countershaft 3, asecond countershaft 4, and a reverse gear shaft 5 are rotatably mounted.The input shaft 2 has five gears 6, 7, 8, 9, 10 (FIG. 1), of which thegear 6, 7, 8 and 9 are non-rotatably fixed, while the gear 10 is adisengageable gear, i.e. it is rotatably mounted on the shaft 2 and canbe locked in a conventional manner by means of an engaging sleeve 12with associated synchronizing means. The countershafts have gear 15, 16,17, 18, 19 (FIG. 1), of which the gears 15, 16, 17 and 18 aredisengageable, being locked to their shafts by means of engaging sleeves21 or 22 with associated synchronizing means. The reverse gear shaft 5has a disengageable gear 23, which can be locked to the shaft by meansof an engaging sleeve 24 with associated synchronizing means.

On the intermediate shafts 3 and 4, a pair of gears 25 and 26 of equalsize are non-rotatably fixed, and engage the crown-wheel 27 of a finaldrive unit, generally designated 28, in the form of a differential. Agear 29 is non-rotatably fixed to the reverse shaft 5. The gear 29 has asomewhat smaller diameter than the gears 25 and 26 and also engages thecrown-wheel 27 of the final drive unit 28.

It is evident from FIGS. 1 and 2 which gears engage each other in therespective gear speeds; only the torque transmission in the first gearspeed and in reverse will be described in detail here. With the gear 15locked to the countershaft 4 by means of the engaging sleeve 22 and withthe other disengageable gears disengaged, the highest gear ratio isobtained for forward drive, i.e. first gear. When shifting from first toreverse, the gear 17 is disengaged and the reversing gear 23 is insteadengaged by means of the engaging sleeve 24, and the disengageable gear17 for the first gear speed, which engages the reverse gear 23, servesas an idler gear to impart to the reverse shaft 5 a direction ofrotation opposite to the rotational direction of the countershafts 3, 4when driving forward.

By placing the reverse gear 23 on a fourth shaft 5, the five-speedgearbox can be made even shorter than the very shortest known five-speedgearbox.

A six-speed embodiment of the gearbox according to the invention, whichis shown in FIG. 2 and which will be described below, can be achieved bybuilding onto the five-speed gearbox. The length of the six-speedgearbox does not need to exceed the length of the shortest knownfive-speed gearbox. In FIG. 2, all of the components with counterpartsin FIG. 1 have been given the same reference numerals as in FIG. 1.Differences in size between the disengageable gears and the gears forthe gear speeds 1-5 and reverse, which result in differences in gearratios between the two types, will not be regarded here.

The gearbox shown in FIG. 2 has a somewhat longer input shaft 2 andcountershaft 4 than the gearbox in FIG. 1. A gear 11 is freely rotatablymounted on the extension of the input shaft 2. Said gear 11 is lockableonto the shaft by means of the same engaging sleeve 12 which locks thegear 10. Via the engaged gear 11 and a gear 20 fixed to an extension ofthe countershaft 4 as well as the gear 26, torque is transmitted in thethird gear speed. In this example, the gear 10 transmits torque in thefourth gear speed. Torque in fifth and sixth gear speed is transmittedby the disengageable gears 16 and 15, respectively, on the countershaft3.

The invention has been described above with reference to preferredembodiments for a transverse engine, but the principle of the inventioncan of course also be applied to a gearbox for a longitudinally mountedengine. An advantage of using the disengageable gear 17 for the firstgear speed as an intermediate gear for reverse is that a high gear ratiois obtained. The same gears are also used for those gear speeds (firstand reverse) on which the same requirements are placed as regardstorque, gear ratio, noise level etc.

I claim:
 1. Motor vehicle gearbox comprising a housing with an input shaft and two countershafts lying in a plane offset from the input shaft and having gears in engagement with gears on the input shaft, at least one gear of each pair of mutually engaging gears on said shafts being disengageable from its shaft, one of said disengageable gears being mounted on one countershaft and being disposed to transmit torque in a first gear speed to a final drive unit, wherein the input shaft (2) has at least five gears (7-11) in engagement with gears (15, 16, 17-20) on the countershafts (3, 4) for transferring torque to the final drive unit for forward drive with at least five different gear ratios and wherein each of said at least five gears on the input shaft meshes with only one of said gears on only one of the countershafts, so that only one power path is provided for each of said at least five different gear ratios, and wherein the one of said disengageable gears (17) for transmitting torque in the first gear speed engages an additional gear (23), which is disengageably carried on a fourth shaft (5) and is disposed to transmit reversing torque to the final drive unit (28) and wherein the countershafts (3, 4) and the fourth shaft (5) have final drive gears (25, 26, 29) non-rotatably joined to their respective shafts, each of said final drive gears engaging a crown wheel (27) of a differential (28).
 2. Gearbox according to claim 1, characterized in that the input shaft (2) and the countershafts (3, 4) have six pairs of interengaging gears (7-11, 15, 17-20) for transmitting torque in a first to a sixth gear speed.
 3. Gearbox according to claim 1, wherein the additional gear (23) on the fourth shaft (5) can be locked to the fourth shaft by means of an engaging device (24) with synchronizing means. 